In July 2011, the International Association of Plumbing and Mechanical Officials (IAPMO) and the American Society of Plumbing Engineers (ASPE) convened a special task force to revise the methodology for properly estimating premise water supply demands in response to the increased use of water-conserving plumbing fixtures, fixture fittings and appliances and the subsequent decreased demand for water in commercial buildings and residences. In collaboration with IAPMO and ASPE, the Water Quality Research Foundation (WQRF) became a co-sponsor in funding the research project. The Pipe Sizing Task Group was organized with three members from ASPE who specialized in statistics and mathematics (later reduced to two members). An additional member from the University of Cincinnati joined this effort.
The Pipe Sizing Task Group recognized that acquisition and analysis of high resolution water use data was a vital first step in the investigation to develop a probability model for predicting peak water demands in buildings. The task group initiated talks with Aquacraft, Inc. to access the largest U.S. database containing residential end uses of water surveys (REUWS). With sponsorship, the task group contracted a specially designed water use database containing parameters to determine fixture use probabilities and flow rates. Because the dataset provided statistics for residential end use only, the scope of work was narrowed to single and multi-family residential dwellings.
Since the water supply flow rate to plumbing fixtures is today significantly less than the flows used in developing the original Hunter’s curve, the scope of the work was further narrowed to determine fixture use probabilities and flow rates only for indoor water-conserving plumbing fixtures. Residential indoor efficient fixtures considered in the database were toilets, showers, dishwashers, clothes washers, and faucets (kitchen and lavatory). Bathtubs were also included but are not considered water-conserving since there are no design benefits to low-flow tub spouts.
The charge of the task group was to develop a statistically based probability model that would predict the peak water demand for single and multi-family dwellings having water-conserving plumbing fixtures. This model would be used to predict the peak water demand for the building supply and principal branches and risers of a residential plumbing system.
